The present invention claims priority to its priority document No. 2002-149632 filed in the Japanese Patent Office on May 23, 2002, the entire contents of which being incorporated by reference herein.
1. Field of the Invention
The present invention relates to a magnetic recording medium and a method of fabricating the same, and in particular to a magnetic recording medium which is capable of ensuring itself and a magnetic head used for recording and/or reproduction thereto and therefrom with improved durability and electromagnetic conversion characteristics, so as to be suitably adopted to high-density magnetic recording.
2. Description of the Related Art
Raising of recording density of magnetic recording media generally demands improvement in the frequency characteristics depending on a higher coercive force and a smoother surface, where a critical problem resides in how successfully the durability can be improved while keeping a desirable level of signal-to-noise ratio (S/N ratio).
For this purpose, various improvements and approaches have been made. A number of proposals include a method of precisely producing projections by forming a high-precision pattern on a non-magnetic support (Japanese Laid-Open Patent Publication No. 10-55535), and a method of producing fine projections by allowing a portion of grains contained in a magnetic layer to expose (Japanese Patent No. 2512005).
However for a case where fine projections are formed on a surface of a non-magnetic support, and a magnetic layer and a non-magnetic protective layer are further formed on the surface having such projections to thereby produce on a surface thereof, that is on a surface of a magnetic recording medium, new fine projections conforming to the fine projections previously formed on the surface of the support, the magnetic layer can gradually be exposed as the projections wear, since the magnetic layer is composed so as to be entangled into the projections on the surface of the medium. If the magnetic layer is thus exposed, grains in the magnetic layer will be more likely to be removed, and the magnetic layer begins to decompose from such portion.
For a case where the projections are formed by fine grains, it is practically difficult to produce really fine projections since the grains tend to coagulate, and this eventually increases spacing loss with regard to a magnetic head.
The present invention is to provide a magnetic recording medium capable of reducing the spacing loss, improving durability, and further capable of improving reliability and electromagnetic conversion characteristics of a magnetic head used with the magnetic recording medium.
A magnetic recording medium of the present invention is composed so as to have a magnetic layer, a non-magnetic protective layer having projected portions formed thereon in a discrete manner according to a thickness distribution, and a lubricant layer, sequentially stacked on a non-magnetic support to have a surface projection formed thereon. That is, in the present invention, the projected portions are formed onto the non-magnetic protective layer which is intrinsically provided on the magnetic layer typically for the purpose of rust prevention of the magnetic layer. The non-magnetic protective layer composing the projected portions can be formed directly on the magnetic layer, and the entire portion thereof including the.projected portions can be composed of the same material. The non-magnetic protective layer can be composed as having a stacked structure of a first non-magnetic protective layer and a second non-magnetic protective layer, and the projected portions can be formed in a discrete manner according to a thickness distribution by the first and second non-magnetic protective layers, where either one of these non-magnetic protective layers is formed in a discontinuous and discrete manner.
Or, the non-magnetic protective layer may be formed so as to extend over a discontinuous metal layer which is formed on the magnetic layer, and so as to form the projected portion according to a thickness distribution of such non-magnetic protective layer. This successfully composes the non-magnetic protective layer, inclusive of the projected portions, with the same material. The discontinuous metal layer herein is composed of a metal having an electric conductivity higher than that of the magnetic layer, and portions with the non-magnetic protective layer formed on the metal layer is made thicker than portions with the non-magnetic protective layer directly formed on the magnetic layer without having the metal layer therebetween. This produces the thickness distribution of the non-magnetic protective layer. That is, the projected portions are limitedly formed only on the discontinuous metal layer.
A method of fabricating a magnetic recording medium of the present invention comprises a step of forming a magnetic layer on a non-magnetic support, a step of forming a non-magnetic protective layer having projected portions formed thereon in a discrete manner according to a thickness distribution, coming next to the step for forming the magnetic layer, and a step of forming a lubricant layer.
The step for forming the non-magnetic protective layer having the projected portions formed thereon in a discrete manner further comprises a step of forming a first non-magnetic protective layer and a step of forming a second non-magnetic protective layer. In the step, either one of the steps, typically the step for forming a lower non-magnetic protective layer herein, is dedicated for formation over the entire surface, and the other step is dedicated for formation in a discrete manner based on mask processing. The non-magnetic protective layer having a thickness distribution can thus be formed with portions where the first and second non-magnetic protective layers are stacked and portions composed only of a single layer, that is, either one of the first and second non-magnetic layers. The thicker portions thus obtained serve as the projected portions.
In another method of the present invention, the step of forming the non-magnetic protective layer having formed thereon the projected portions further comprises a step of forming a discontinuous metal layer having an electric conductivity higher than that of the magnetic layer, and a step of forming a non-magnetic protective layer over the entire surface so as to cover also the discontinuous metal layer as well as the magnetic layer. The projected portions are formed based on difference in the growth speed of the non-magnetic protective layer between areas having the discontinuous metal layer and areas having no discontinuous metal layer but exposing the magnetic layer within through-holes. The non-magnetic protective layer is made thicker at portions on the discontinuous metal layer, and the thicker portions serve as the projected portions.
In other words, the present invention is to produce necessary surface projections on the surface of the magnetic layer by forming the projected portions not on the non-magnetic support or on the magnetic layer formed thereon as in the conventional technique, but instead on the non-magnetic protective layer formed on the magnetic layer.
In the method of fabricating a magnetic recording medium of the present invention, the non-magnetic protective layer having projected portions formed thereon is formed after the step of forming the magnetic layer on the non-magnetic support.
That is, in the magnetic recording medium and a method of fabricating a magnetic recording medium of the present invention, the projected portions are formed on the non-magnetic protective layer in a discrete manner irrespective of the constitution of the magnetic layer per se and of fabrication method. This is successful in avoiding adverse effects of the projected portions on the characteristics of the magnetic layer and durability.
As described in the above, in the magnetic recording medium of the present invention, the projected portions become less likely to drop off since the projected portions are formed based on the thickness distribution of the non-magnetic protective layer, and since the entire portion of the non-magnetic protective layer inclusive of such projected portions is composed of the same material. The magnetic recording medium of the present invention having no magnetic layer in the projected portions, unlike the conventional constitution, is also successful in effectively avoiding destruction of the magnetic layer even if the projected portions should wear under sliding contact with a magnetic head, and in improving running ability and durability.
According to the method of fabricating a magnetic recording medium of the present invention, the height of the projected portions can precisely be controlled. This successfully composes the magnetic recording medium having a small spacing loss and excellent electro-magnetic conversion characteristics.